This invention relates to the identification of fatty acid or lipid amides as ligands of the G-protein coupled receptor OSGPR116, and is directed to in vitro methods for screening candidate drugs for their ability to modulate the activity of OSGPR116, and to methods of treating disease by administering to an individual a therapeutic amount of a modulator of OSGPR116.
G-protein coupled receptors (GPCRs) are a super-family of membrane receptors that mediate a wide variety of biological functions. Upon binding of extracellular ligands, GPCRs interact with a specific subset of heterotrimeric G proteins that can, in their activated forms, inhibit or activate various effector enzymes and/or ion channels. All GPCRs are predicted to share a common molecular architecture consisting of seven transmembrane helices linked by alternating intracellular and extracellular loops. The extracellular receptor surface has been shown to be involved in ligand binding whereas the intracellular portions are involved in G-protein recognition and activation. Different G-protein alpha-subunits, and beta-gamma subunit complexes, preferentially stimulate or inhibit particular effector molecules to modulate various biological functions in a cell. Typical effector molecules include adenylate cyclase, phospholipases C and A2, cGMP phosphodiesterase-γ, and potassium, sodium and calcium channels. Additional regulation of GPCR activity is thought to occur via receptor oligomerization and interaction with the protein β-arrestin (e.g. see Rocheville, M. et. al. (2000) Science 288:154–157; Gether, U. (2000) Endocrine Reviews 21:90–113; Luttrel, L. M. et. al. (1999) Science 283:655–661). G-protein coupled receptors are found ubiquitously in all cell types within mammalian organisms. Many therapeutic agents targeting GPCR receptors have been successfully introduced onto the market, thereby establishing their value as targets for drug discovery and development (e.g. Wise, A. et al. 2002, DDT, 7:235–246). Over 30% of clinically marketed drugs are active on GPCRs.
It has been estimated that for about 40% of GPCRs in the human genome (excluding sensory receptors) the ligand remains unknown. Such GPCRs are commonly referred to as “orphan” receptors. For example, the primary structures of the human, rat and mouse forms of the orphan GPCR OSGPR116 (also known as OSGPR116) were recently described in two recent U.S. patents (U.S. Pat. No. 6,221,660, U.S. Pat. No. 6,468,756). In these patents the ligand for OSGPR116 was described as all-trans retinoic acid, which was shown to stimulate the production of cyclic AMP in host cells expressing recombinant receptor. OSGPR116 was described as a valuable tool for designing drugs for the treatment of over fifty diverse pathophysiological conditions, including obesity.
There is unquestionably a great unmet need for new drugs for the treatment of obesity, and thus amelioration of diseases associated with this condition, e.g. diabetes, cardiovascular diseases. Currently, more than 44 million Americans are considered obese by BMI index; that is, have a Body Mass Index (Kg/m2) greater than or equal to 30. This reflects an increase of 74 percent since 1991. Pharmaceutical research has explored agents with a variety of mechanisms of action as potential anti-obesity drugs, e.g. Orlistat, which reduces the absorption of dietary fat, and is a pancreatic lipase inhibitor; and Sibutramine, an appetite suppressant, and an inhibitor of the reuptake of noradrenaline and serotonin. Additional appetite suppressants dexfenfluramine, fenfluramine and, phentermine have been withdrawn following reports of valvular heart disease associated with their use; these drugs were also associated with the rare but serious risk of pulmonary hypertension. However, appetite suppressant continue to be an attractive category for discovery, and more recently fatty acid ethanolamide compounds have shown promise as agents to inhibit food intake (WO 02/080860; de Fonseca, F. R. et.al. (2001) Nature, 414:209–212). However, the molecular mechanism of fatty acid ethanolamides in modulating food intake has not been elucidated. Consequently there are considerable problems associated with developing such compounds of unknown mechanism of action. This problem has now been resolved with the surprising discovery that such fatty acid ethanolamide compounds are ligands of OSGPR116, thus providing a mechanism of action, and a basis for further assay and compound development.